An article from the "Interagency Ecological Program (IEP) for the Sacramento-San Joaquin Estuary" Newsletter (Vol.11, No.1 --Winter 1998)

A measurement of the quantity of water flowing from the Sacramento-San Joaquin Delta into Suisun Bay (Delta outflow) has been desired by those studying and managing the San Francisco Bay/Delta estuary since the 1920's.

Historically, Delta outflow has been estimated using a mass-balance calculation that uses measured Delta inflows and exports, and imprecise estimates of consumptive use for the approximately 1,800 small agricultural diversions within the Delta.

Although the mass-balance method has worked reasonably well over the years, it has several shortcomings.

The USGS can now provide indirect measurements of Delta outflow by combining flow measurements from 4 of the 10 continuous flow monitoring stations currently operated by the USGS in the Delta.

During the 1960s and 1970s, data collected in Suisun Bay were analyzed to develop a conceptual model of how water, salt, and sediment move within and through the Bay.

This conceptual model has been used to manage freshwater flows from the Sacramento-San Joaquin Delta to Suisun Bay to improve habitat for several threatened and endangered fish species.

Instrumentation used to measure water velocity, salinity, and suspended-solids concentration (SSC) greatly improved during the 1980s and 1990s.

The U.S. Geological Survey (USGS) has utilized these new instruments to collect one of the largest, high-quality hydrodynamic and sediment data sets available for any estuary. Analysis of these new data has led to the revision of the conceptual model of circulation and sediment transport in Suisun Bay.